The present invention relates to a variable rate communication system which is applied to the wireless communication system, etc., of the CDMA (Code Division Multiple Access) method, for example, and can selectively use either of a predetermined plurality of data rates determined in stages by a frame unit with a transmission device and a transmission device and a reception device used with this variable rate communication system.
A wireless communication system of a CDMA method can selectively use either of a plurality of predetermined data rates of, for example, 9600 bps, 4800 bps, 2400 bps, and 1200 bps provided in stages by a frame unit with a transmission device. After performing processing of making a convolutional code according to a selected data rate to a transmission data, the transmission device transmits data.
All Viterbi decoding processings according to each of the plural data rates are executed to a reception data on a reception side. The symbol error rate in each reception data after decoding processes is measured respectively. The data rate corresponding to the Viterbi decoding processing performed to obtain the reception data in which this symbol error rate becomes minimum among a plurality of data rates is assumed to be a correct symbol rate.
However, since the Viterbi decoding processing needs quite a lot of calculations, if the Viterbi decoding processing according to each data rate is performed to the time-division, quite a lot of time is spent in the judgment of the data rate. The judgment of the data rate can be promptly performed if the Viterbi decoding processing according to each data rate is performed in parallel. However, the consumption electric power increases in this case since the operation of a lot of processing sections are operated at the same time.
As mentioned above conventional system, since the decoding processing according to all the data rates must be performed respectively on the reception side, there are disadvantages that the processing time is long, and the consumption electric power is large.
An object of the present invention is to provide a variable rate communication system and a transmission device and a reception device applied thereto which reduce the amount of processings for judgment of the data rate, and can shorten a time required to judge the data rate and decrease a consumption electric power.
To achieve the above-mentioned object, a variable rate communication system according to the present invention comprises a transmission device capable of selectively using one of a predetermined plurality of data rates for each frame determined in stages; and a reception device capable of receiving data transmitted by the plurality of data rates, in which the transmission device comprises: data rate decision means decides a data rate used with the latest frame to one of data rates used with the frame immediately before and a different data rate from a data rate used with the frame immediately before by one stage; and encoding means for performing a predetermined encoding processing according to the data rate decided by the data rate decision means to a transmission data, and the reception device comprises: decoding means for performing a predetermined decoding processing according to the plurality of data rates to a reception data, respectively; narrowing means for narrowing a candidates of the data rates used with a received latest frame to a part of the plurality of data rates based on a data rate at least used with a frame immediately before; judgment processing means for performing a predetermined judgment processing to judge a data rate used with the latest frame as valid data rates for the narrowed data rates; and reception data selection means for selecting a reception data to which a decoding processing according to a data rate judged by the judgment processing means is performed by the decoding means as a valid reception data. For example, the encoding means is a convolutional coding processing etc. The decoding processing is, for example, a Viterbi decoding processing etc., and the decoding means consists of, for example, a plurality of Viterbi decoders.
Since the transmission device determines the data rates used with the latest frame in either a data rate used with the frame immediately before or different data rate from a data rate used with the frame immediately before by one stage, the reception device can narrow the candidate of the data rates used with the received latest frame partially of the plurality of data rates based on the data rate at least used with the frame immediately before. Therefore, the processing amount of the judgment processing is decreased by performing the predetermined judgment processing for judging the data rate used for the latest frame for only this narrowed data rate.
Another present invention is to provides a reception device, which receives a frame transmitted from a transmission device which is selectively usable one of a plurality of predetermined data rates defined in stages for each frame, comprising: priority setting means for setting a priority to the data rates narrowed by the narrowing means; re-encoding means for performing a predetermined encoding processing according to each of the plurality of data rates to the reception data, respectively; re-encoding means for performing the encoding processing according to each of the plurality of data rates to the reception data after the decoding processing according to the same data rate is performed by the decoding means, respectively; data rate judgment means for obtaining an error rate to the received data before decoding by the decoding means regarding to the re-encoded data re-encoded by the re-encoding means, and for judging a data rate corresponding to the encoding processing performed to obtain the re-encoded data as a data rate which is used with the latest frame when this error rate is smaller than a predetermined value; data rate judgment control means for setting one of the plurality of data rates in a test rate, and for making a decoding processing and a re-encoding processing according to the test rate, and a judgment processing by the data rate judgment means until the data rate used with the latest frame is judged by the data rate judgment means with changing in order with a high priority to which the data rate to be a test rate is set by the priority setting means; and reception data selection means for selecting a reception data to which a decoding processing according to a data rate judged by the judgment processing means is performed by the decoding means as a valid reception data. For example, the re-encoding means is a convolutional coding processing etc. For example, the reception data selection means consists of a buffer and a reception data output control means.
Since the judgment processing whether it is a data rate used with the latest frame need not be performed concerning all the data rates even if the lowest rank priority is set to the data rate used with the latest frame, the amount of processing is decreased. Moreover, since the priority is set based on the data rate at least used with the frame immediately before, a relatively high-ranking priority can be set to the data rate used with the latest frame in many cases, and the judgment processing whether it is a data rate used with the latest frame only to very few data rates may be performed.
As described above, according to the present invention, it becomes possible to reduce the processing amount for the judgment of the data rate, to achieve shortening time which requires to judge the data rate and to decrease the power consumption.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.